It's very much a matter of personal preference - the Loupe is one thing I prefer about Aperture, others being the smart albums and stacks' more visual appearance (it's public knowledge that stacks and versions will be in Lightroom v1). Otherwise I find the interface was very fiddly with controls scattered all around the screen, and messy too with two interface styles in one program, duplication of palettes, and at least 4 styles of button being used. That fiddly character really hits home with large numbers of pictures and Lightroom's Quick Develop and Develop tools are much cleaner and more efficient. Export processes also lock up the program. But so many things are close calls - so I hate being unable to hide Aperture's filmstrip except in black hole mode, yet like being able to move it below or to one side of the image which I can't do in Lightroom. And I love that Loupe.
They've also still got work to do to make Aperture acceptable from a DAM perspective. They've graciously allowed you to leave your files where you want, but you still have to be too careful or it will salt them away into its library package. And apart from the program being limited to the Mac, the export procedure is still a barrier. With any program which has DAM aspirations, you have to be sure up front of the exit route.
The world looks so beautiful through the windows, who needs Jobs (or silly straplines)?